i1 : X = specialFourfold random({5:{1}},0_(PP_(ZZ/33331)^7));
o1 : ProjectiveVariety, complete intersection of three quadrics in PP^7 containing a surface of degree 1 and sectional genus 0

i2 : describe X
o2 = Complete intersection of 3 quadrics in PP^7
of discriminant 31 = det 8 1 
 1 4 
containing a surface of degree 1 and sectional genus 0
cut out by 5 hypersurfaces of degree 1
(This is a classical example of rational fourfold)

i3 : time U' = associatedCastelnuovoSurface X;
 used 5.93437s (cpu); 2.21093s (thread); 0s (gc)
o3 : ProjectiveVariety, Castelnuovo surface associated to X

i4 : (mu,U,C,f) = building U';

i5 : ? mu
o5 = multirational map consisting of one single rational map
source variety: 5dimensional subvariety of PP^7 cut out by 2 hypersurfaces of degree 2
target variety: PP^4
dominance: true
